It is known that the pilot of an airplane has available different correction or monitoring means to meet the meeting point and this, according to different associated energy levels. There can be conventional means such as engines and airbrakes, but also other means linked to the dynamical configuration of the airplane, such as the slats and flaps and the landing gear which also impact on the airplane performances and, consequently, on its capacities to modify the energy thereof. Still three other so-called operational means can be mentioned, namely the modification of the vertical plan, based more on the notion of energy distribution between kinetic energy and potential energy, the modification of the lateral plan, allowing the ground trace to be adjusted and the airplane energy situation to thus be adapted with the setpoint and finally the modification of the setpoint speed servo-controlled by the self-thrust.
The present invention applies more particularly to the position control of the slats and flaps (defining the aerodynamic configuration of the airplane) and to the position control of the landing gear.
For the approach cases, whatever the piloting mode being considered (manual, managed, selected), the command of the different aerodynamic configurations and of the landing gear always stays manual and under the responsibility of the pilot. In particular, the pilot controls the extension of the slats and flaps manually with the help of a lever provided for this purpose. The extension of the slats and flaps having a direct impact on the airplane performance, the pilot must plan such extension as a function of the flied trajectory and of the targeted setpoint speed.
On the present airplanes, the slat and flap configuration changes are decided by comparison between the airplane speed and characteristic speeds expressed in calibrated speed CAS. Such operational speeds are the following:                a minimum operational speed in a smooth configuration (so-called “green dot speed”). Switching into configuration 1 generally occurs at such speed. This speed specifically offers the best fineness in a smooth configuration. It depends on the altitude and the mass of the airplane;        a recommended speed (so-called “S-speed”) to control the configuration 2. This speed depends on the minimum monitoring speed VMCL (minimum monitoring speed), on the speed VS1g (minimum speed to maintain a uniform rectilinear flight) in a configuration 1 and on the speed VFE (maximum speed under which the configuration can be activated) in a configuration 2;        a recommended speed (so-called “F2-speed”) so as to control the configuration 3. Such a speed depends on the minimum monitoring speed VMCL, on the speed VS1g in a configuration 2 and on the speed VFE in a so-called “full” configuration; and        a recommended speed (so-called “F3-speed”) to control the so-called “full” configuration. Such speed depends on the monitoring minimum speed VMCL, on the speed VS1g in a configuration 3 and on the speed VFE in a so-called “full” configuration.        
Conventionally, according to the invention, the extension of the landing gear is controlled as soon as the configuration 2 is extended. Nevertheless, generally speaking, the landing gear can be used under the so-called DLO speed (maximum speed under which the landing gear can be extended).
Consequently, in spite of an increasing automation on the airplanes, some actuators, amongst others the actuators of the slats, the flaps and the landing gear, only stay usable in the manual way.
Thus, in order to help the pilot to take a decision or to inform the pilot about the current energy state of the airplane, it is known from the document U.S. Patent Publication No. 2008/0140272 a solution allowing the over-energy situations to be anticipated. The object of such a solution is to display two energy prediction circles on an interface ND (“Navigation Display”) of the cockpit so as to inform the pilot about its energy state predicted at the level of the runway threshold. Both calculated predictions consider the hypothesis of a standard descent (standard trajectory with a standard deceleration step, extension of the aerodynamic configurations and of the landing gear according to the standard procedure) and a limit descent (anticipated extension of the aerodynamic configurations, anticipated train extension, maximum extended airbrakes). Thanks to the representation of such circles, the pilot can anticipate the under- or over-energy state by using respectively the engines or the airbrakes and can thus bring back the airplane toward an acceptable energy state. Such solution presents the interest to inform the pilot about its energy state, however the correction to be applied stays at the pilot's charge. Moreover, the energy circles are based on two trajectory types (extreme trajectories) and do not provide any precise indication for other types of intermediate trajectory.
Consequently various problems are to be solved:                to inform the pilot about its energy state throughout its trajectory up to a final objective. The solution proposed by the document US-2008/0140272 is of a great utility upon the descent phase until the deceleration point, but it only presupposes two package ways of piloting the airplane and does not provide itself the implementation of the airplane piloting;        to help the pilot in his decision taking. Upon non nominal situations (in case of wind, over-energy, under-energy), the pilot must use his know-how to adapt the airplane piloting to the changing external surroundings and to the current performances of the airplane. The pilot must call on his own experience to estimate the effect of the use of different actuators on the coming energy state. Such estimate stays however imprecise and not optimal;        to reduce the working charge of the pilot. In fact, as indicated above, several actuators must be manually adjusted.        